1. Field of the Invention
The present invention relates to a sheet convey apparatus for automatically supplying and discharging a sheet to and from a treatment portion. More particularly, the present invention relates to a sheet convey apparatus adapted to automatically supply and discharge a sheet with respect to an image reading portion of an image forming apparatus such as a copying machine, laser beam printer (LBP), image reading apparatus, image recording apparatus and the like, and an image forming apparatus having such a sheet convey apparatus.
2. Related Background Art
FIG. 13 shows an example of a conventional sheet convey apparatus. The sheet convey apparatus shown in this example is an original (document) feed apparatus (ADF).
In FIG. 13, a platen glass 2 acting as an image reading treatment portion is fixed to an upper surface of a body 1 of an image forming apparatus such as a copying machine, LBP and the like. An internal construction of the image forming apparatus will be described later.
An original convey apparatus including the platen glass 2 is generally designated by the reference numeral 3 and is mounted on the upper surface of the image forming apparatus. The original convey apparatus 3 comprises an outer cover (main cover) 4, and an original tray 5 acting as an original stacking plate on which sheet originals S are stacked in such a manner that leading or tip ends of the sheet originals are inserted in an original inlet portion 20.
When a semi-circular sheet supply roller 6 is rotated in response to an original supply start signal, a positive feeding force is applied to a lowermost sheet original of the sheet original stack S on the original tray 5, and the lowermost sheet original alone is separated from the other sheet originals at a separation and supply portion comprising a feed roller 7 and a separation belt 8, and the separated sheet original is supplied into the original convey apparatus 3. The separated sheet original passes through a sheet path a, a pair of register rollers 9 and a sheet path b, and is sent between the platen glass 2 and a rotatable original convey belt 10.
The pair of register rollers 9 serve to correct the skew-feed of the sheet original by abutting the tip end of the sheet original against a nip between the rollers and also to provide the sheet supply timing with respect to the platen glass 2.
The rotatable original convey belt 10 serves to convey the sheet original on the platen glass 2, and extends between and wound around a drive roller 11 disposed at a left end of the platen glass 2 and a turn roller 12 disposed at a right end of the platen glass 2 in such a manner that a lower running belt portion is urged against the platen glass 2 by a plurality of urging rollers 13. The original convey belt 10 is rotated in an anti-clockwise direction shown by the arrow so that the sheet original conveyed between the platen glass 2 and the belt 10 from the sheet path b is conveyed along a sheet path c between the platen glass 2 and the belt 10 from the left to the right of the platen glass 2 while sliding on the platen glass. When the sheet original is conveyed to a predetermined set position on the platen glass, the original convey belt 10 is stopped, thereby automatically setting the sheet original at the predetermined set position. Then, image information on the sheet original set on the platen glass is read by a reading mechanism of the image forming apparatus. When the reading treatment is finished, the original convey belt 10 is rotated in the counter-clockwise direction again to shift the sheet original to the right along the upper surface of the platen glass 2. Then, the sheet original is discharged onto a discharge tray 16 disposed between the original tray 5 and the original convey belt 10 through a sheet path d, a pair of discharge rollers 14 and a discharge opening 15.
In this way, a cycle wherein the sheet originals S are successively supplied from the original tray 5 to the platen glass 2 one by one and are read on the platen glass and then are discharged onto the discharge tray 16 successively is automatically performed.
FIG. 14 shows another example of a conventional original convey apparatus (recirculating document feeder, i.e., RDF). The same constructual elements as those shown in FIG. 13 are designated by the same reference numerals and explanation thereof will be omitted.
As is in the apparatus shown in FIG. 13, sheet originals S stacked on an original tray 5 are separated one by one from the lowermost one by a sheet supply roller 6 and separation and supply portion 7, 8, and the separated sheet original is automatically conveyed to a platen glass 2 through a sheet path a, a pair of regist rollers 9 and a sheet path b to be set on the platen glass at a predetermined position. Then, image information on the sheet original is read. When the reading treatment is finished, a rotatable original convey belt 10 is rotated reversely in a clockwise direction to return the sheet original on the platen glass 2 to the left to introduce the sheet original into a return sheet path e. Then, the sheet original is discharged onto the non-treated sheet original stack S on the original tray 5 through a reverse rotation path f along a large reverse rotation roller 17, a discharge path g, a pair of discharge rollers 14 and a discharge opening 15.
A first supply, reading treatment and discharge cycle for the sheet originals S stacked on the original tray 5 is completed, a new supply, reading treatment and discharge cycle for the sheet originals returned onto the original tray 5 is started. In this way, a predetermined number of original convey circulations are carried out. In FIG. 14, there are provided a sheet path switching flapper 19 and a branch sheet path h. In case of both-face imaged sheet originals, each sheet original a first face of which was read is introduced from the reverse rotation path f to the branch sheet path h, so that the sheet original is re-supplied to the platen glass 2 with a second face thereof facing downwardly. Incidentally, urging rollers 18 serve to urge the sheet original against the large reverse rotation roller 17.
However, in the above conventional sheet convey apparatus as shown in FIG. 13, since an upper space above the discharge tray 16 is limited because of the presence of the original tray (sheet stacking plate) 5, the number of sheet originals to be treated is limited. If the number of sheet originals to be treated is increased, the apparatus becomes large-sized accordingly.
On the other hand, in the conventional sheet convey apparatus as shown in FIG. 14, since it is of circulating type, it is necessary to improve the re-supplying ability for re-supplying the sheet originals from the original tray 5, with the result that the original tray must be arranged with a large inclination angle, thereby making the apparatus large-sized.